If your dad is the only one in the family to have cancer, his cancer is probably not genetic.
Signs of a possible genetic cancer are: the same or related cancers in more than one family member, especially in more than one generation and cancer diagnosis at an early age (under 50); diagnosis at earlier ages in succeeding generations.
If you do have any of these signs of hereditary cancer in your family, your might want to talk to your doctor about screening tests for these cancers for you and your sister.